Phase coherence weighted multi-mode total focusing method imaging of multi-angle defects

The multi-mode total focusing method (MTFM) enables a region of interest within a specimen to be imaged using different combinations of beam paths and wave-mode. For a crack, the diffraction response of the tip may be evident in certain modes and the specular reflection in others. Accurate characterisation of defects requires combining information from multiple modes. For MTFM images, not all modes have a high signal-to-noise ratio (SNR). In this work, multi-mode phase coherence imaging (MPCI) was proposed by combining MTFM and phase coherence imaging (PCI) method. The better data fusion is mainly the result of the selective use of information from the most appropriate mode(s) and fusion reduces the probability of misjudging defects. In this paper, full matrix data was acquired for aluminium alloy blocks containing notch defects at different angles and imaged using the both multi-mode methods. The signal-to-noise ratio results of the two multimodal methods show that MPCI is better than MTFM for multi-angle defect detection. In addition, the Sobol sensitivity analysis method was used to construct the signal-to-noise ratio sensitivity parameter for quantifying the imaging effect of each mode on defects at different angles, and the results can effectively guide the optimisation of the multi-mode fusion algorithm.